Production of regenerated cellulose filaments



March 14, 1961 DRAW-OFF SPEEDWN METRES PER MlNUTE N E. E. TALLIS ET AL 2,975,023

PRODUCTION OF REGENERATED CELLULOSE FILAMENTS Filed June 25, 1958 I I F I 100 2 00 300 400 500 SEcoNDS BALL FALL VISCOSITY //71/e/7/0/$ .Emeg/ Edward E/fls DawdMc/za/son 549/ By f/ve/k af/omeys PRODUCTION OF REGENERATED CELLULOSE FILAMENTS Ernest Edward Tallis and David Nicholson Tyler, Coventry, England, assignors to Courtaulds Limited, London, England, a British company Filed June 23, 1958, Ser. No. 743,720 Claims priority, application Great Britain June 28, 1957 11 Claims. (11. 18-54) This invention relates to the production of regenerated cellulose filaments and the like from viscose and particularly to the rapid production of such filaments having a high tenacity and which can be twisted into high strength viscose rayon cords.

The tenacity of regenerated cellulose fibres can be increased by subjecting them immediately after spinning to stretching in a hot dilute acid bath, as described in US, patent specification No. 2,192,074. As described in the specification of co-pending patent applications Ser. Nos. 581,377 and 582,907, both now abandoned, and of copending application Serial No. 825,624, the addition to the viscose of polyethylene oxide or certain polyethylene oxide condensation products enables filaments to be produced having a thick skin and non-crenulated surface with a bean shaped cross-section and a diffuse boundary between the skin and core. Such filaments have a high wet tenacity and are capable of forming a cord of good tensile properties. The skin and core can be shown, and the skin and core differentiated by a staining technique as described for example in the Textile Research Journal 1945, page 443.

Also, in our co-pending application Ser. No. 629,512 we found that a significant improvement in fibre and cord properties particularly in the conditioned state at 65 percent relative humidity could be obtained by spinning, in the presence of polyethylene oxide or polyethylene oxide condensation products, viscose in which the degree of polymerisation of the cellulose is unusually high. We found however that the benefit of the longer chain length of the cellulose molecules is only obtained when certain spinning conditions are used and, in particular, that for a given value of ball fall viscosity of the viscose there is a critical speed of drawing the threads away from the jet which must not be exceeded if advantage is to be taken of the longer chain length.

Viscose is normally spun at 20 C., although proposals have been made to spin at higher temperatures, but very little advantage is gained in spinning normal viscose under these conditions. However, We have now found that if the viscose made from a cellulose having a high degree of polymerization (DR) and containing polyethylene oxide is extruded at an increased temperature, the drawofi speed of the filaments may be increased substantially, but to an extent limited by the ball-fall viscosity of the viscose at the extrusion temperature if advantage is to be taken of the effect of the high D.P in increasing the tenacity of the filaments. The draw-ofi speed should not substantially exceed the value defined by the curve shown inthe accompanying drawing, the ball fall viscosity being defined as the time taken for a steel ball of one eighth of an inch diameter to fall through 20 centimetres of viscose at the extrusion temperature, draw-oil speed is defined as the speed at which coagulated filaments are drawn through the spinning bath away from the spinnerette.

Patented Mar. 14, 1961 ice According to the invention therefore, regenerated cellulose filaments having a substantially circular or bean-shaped cross-section and a substantially all-skin structure are produced by extruding viscose, the cellulose of which has an average degree of polymerization of at least 400,'at a temperature of between 40 C. and 60 C. and at a salt point between 6 and 15, preferably from 8.5 to 12, into an aqueous coagulating bath containing sulphuric acid together with zinc sulphate and sodium sulphate, the total saltcontent preferably not exceeding 24 percent by weight, in the presence of between 0.5 and 10 percent by weight of the Weight of the cellulose of a polyethylene oxide of average molecular weight between 300 and 10,000, preferably between 600 and 6,000, at a draw off speed not substantially greater than that defined by the curve shown in the accompanying drawing, the ball fall viscosity being defined as the number of seconds taken by a steel ball one eighth of an inch in diameter to fall through 20 centimetres of viscose at the extrusion temperature.

As indicated in the figure, the viscosities used in the present process range from about 40 to about 400 seconds.

To develop high tenacity, the filaments should be subjected to hot-stretching, in accordance with US. patent specification No. 2,192,074 in a hot aqueous acid bath preferably containing at least 3 percent of sulphuric acid. Regeneration of the filaments should be substantially complete when the filaments leave this bath.

The salt point is defined in its normal sense, as the percentage strength of an aqueous sodium chloride solution required just to coagulate the viscose at 15 C.

Where practicable, improved properties are obtained by spinning at an extrusion ratio less than one. The extrusion ratio is the ratio of the speed at which the filaments are drawn from the jet to the speed at which the viscose passes through the jet orifices.

The polyethylene oxide is preferably added to the viscose and may be added in the form of a condensation product as described in the specification of application Ser. No. 582,907.

For any given content of caustic soda in the viscose and spinning speed, the sum of the cellulose content of the viscose and the best concentration of spinning bath acid, both expressed as a percentage, is approximately constant. For example, for a concentration of 7 percent caustic soda and a draw-off speed of 14 metres per minute,

the constant is equal to from 12 to 13.

Preferably, the zinc sulphate concentration in the bath is 6 to 15 percent. The best yarn results have so far been obtained with 6 to 7 percent cellulose, 7 percent soda, 6 to 7 percent acid, 10 percent zinc sulphate, 3 percent polyethylene oxide on the weight of cellulose and an extrusion ratio of 0.7.

In the following examples, proportions are by weight.

Example 1 passed through a coiled lead tube immersed in the spinning bath and was thus heated to 50 C. and its ball fall viscosity reduced to 50 seconds. The draw-oil speed was 25 /2 metres per minute. The yarn was stretched percent through a second bath at 95 C. containing 3.0 percent sulphuric acid and less than 1.5 percent total salts and after washing, drying on a heated drum and collecting, had the following properties:

Denier 1008. Oven dry tenacity 5.95 grams per denier. 'Oven dry extensibility 7.4 percent.

Conditioned tenacity (65 percent relative humidity) -2 p.84 grams per denier. Conditioned extensibility 9.9 percent. Wet tenacity 3.87 grams per denier. Wet extensibility 22.0 percent.

Example 2 Viscose 6.6 percent cellulose of average DP 585, 7.0 percent caustic soda, 3.0 percent polyethylene oxide of average molecular weight 1500. Viscose temperature 20 C. Ball fall viscosity 130 seconds. Extrusion ratio 0.55.

Salt figure 9.8 Draw oir' speed 28 metres per minute. Spin bath 8.0 percent sulphuric acid,

10.0 percent zinc sulphate, 11.0 percent sodium sulphate, 55 C. Stretch 80 percent in bath as first example. The yarn and cord properties were as follows:

Yarn, denier 1675. Oven dry tenacity 5.05 grams per denler. Oven dry extensibility 7.5 percent. Conditioned tenacity (65 percent relative humidity) 4.21 grams per denier. Conditioned extensibility 10.0 percent. Wet tenacity 2.77 grams per denier. Wet extensibility 18.4 percent. 12 S x 12 Z cord, denier 3860. Oven dry breaking load 29.1 lb. Oven dry tenacity 3.42 grams per denier.

Oven dry extensibility It will be seen that the oven dry cord tenacity in the first example is about 36 percent higher than in the second example.

What we claim is:

l. A process for producing regenerated cellulose filaments having a substantially circular or bean shaped cross-section and a substantially all skin structure comprising extruding viscose, the cellulose of said viscose having a degree ofpolymerisation of at least 400, at a temperature of 40 C. to 60 C. at a salt point between 6 and 15, and at an extrusion ratio of less than 1 into an aqueous coagulating bath containing sulphuric acid and zinc sulphate and sodium sulphate, in the presence of between 0.5 and 10 percent by weight of the weight of the cellulose of a polyethylene oxide of average molecular weight between 300 and 10,000 at a draw ofi speed not substantially greater than that defined by the curve shown in the figure accompanying this specification, and at a ball fall viscosity of between about 40 and about 400 seconds, the ball fall viscosity being defined as the number of seconds taken by a steel ball one eighth 11.5 percent.

4 of an inch in diameter to fall through twenty centimetres of viscose at the extrusion temperature.

2. A process according to claim 1, in which upon emerging from the coagulating bath, the filaments are stretched in a hot acid bath.

3. A process according to claim 1 in which the salt point of the viscose is between 8.5 and 12 inclusive.

4. A process according to claim 1, in which the total salt content of the coagulating bath does not exceed 24 percent by weight.

5. A process according to claim 1, in which the average molecular weight of the polyethylene oxide is between 600 and 6,000.

6. A process according to claim 1, in which the polyethylene oxide is added to the viscose.

7. A process according to claim 1, in which the concentration of zinc sulphate in the coagulating bath is from 6 to 15 percent by weight.

8. A process according to claim 4, in which the viscose contains from 6 to 7 percent cellulose, 7 percent caustic soda and 3 percent of polyethylene oxide based on the weight of cellulose, the coagulating bath contains 6 to 7 percent acid, 10 percent zinc sulphate and the extrusion ratio is 0.7.

9. A process according to claim 1, in which the viscose contains not more than 5 percent of cellulose and has a ball fall viscosity of from 25 to 67, the percentage of sulphuric acid in the coagulating bath is from 0.9 to 1.5 times the percentage of caustic soda in the viscose, and the bath contains 3 to 15 percent of zinc sulphate.

10. A process according to claim 10, in which the percentage of sulphuric acid in the coagulating bath is from 1.15 to 1.40 times the percentage of caustic soda in the viscose.

11. Regenerated cellulose filaments having a substantially circular cross section with a smooth skin and an all skin structure produced by extruding viscose, the cellulose of which has a degree of polymerisation of at least 400 at a temperature of 40 C. to 60 C. at a salt point between 6 and 15 and at an extrusion ratio of less than 1 into an aqueous coagulating bath containing sulphuric acid and zinc sulphate and sodium sulphate, in the presence of between 0.5 and 10 percent by weight of the weight of the cellulose of a polyethylene oxide of average molecular weight between 300 and 10,000 at a draw ofi speed not substantially greater than that defined by the curve shown in the figure accompanying this specification and at a ball fall viscosity of between about 40 and about 400 seconds, the ball fall viscosity being defined as the number of seconds taken by a steel ball one eighth of an inch in diameter to fall through twenty centimeters of viscose at the extrusion temperature;

References Cited in the file of this patent UNITED STATES PATENTS Ott, E. Spurlin, H. M. Grafiiin, M. W. High Polymers, vol. V, 2nd edition (1955), pages 13291334.

pAAAA A p Emma- UNITED STATES PATENT OFFICE vCE'RTIIFICATIO N OF CORRECTION Patent No. 2,975 O23 March 14, 1961 Ernest Edward Tallis et a1.

It is Hereby certified that error appears in the ,above .nqmbered petlent requiring correction and"that the said Letters Patent should read'as corrected below.

Column 4, line 31 for the c laim reference numeral "10" read 9 Signed and sealed this 22nd day of August 1961.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

1. A PROCESS FOR PRODUCING REGENERATED CELLULOSE FILAMENTS HAVING A SUBSTANTIALLY CIRCULAR OR BEAN SHAPED CROSS-SECTION ANS A SUBSTANTIALLY ALL SKIN STRUCTURE COMPRISING EXTRUDING VISCOSE, THE CELLULOSE OF SAID VISCOSE HAVING A DEGREE OF POLYMERISATION OF AT LEAST 400, AT A TEMPERATURE OF 40*C. TO 60*C. AT 60*C. AT A SALT POINT BETWEEN 6 AND 15, AND AT AN EXTRUSION RATIO OF LESS THAN 1 INTO AN AQUEOUS COAGULATING BATH CONTAINING SULPHURIC ACID AND ZINC SULPHATE AND SODIUM SULPHATE, IN THE PRESENCE OF BETWEEN 0.5 AND 10 PERCENT BY WEIGHT OF THE WEIGHT OF THE CELLULOSE OF A POLYETHYLENE OXIDE OF AVERAGE MOLECULAR WEIGHT BETWEEN 300 AND 10,000 AT A DRAW OFF SPEED NOT SUBSTANTIALLY GREATER THAN THAT DEFINED BY THE CURVE SHOWN IN THE FIGURE ACCOMPANYING THIS SPECIFICATION, AND AT A BALL FALL VISCOSITY OF BETWEEN ABOUT 40 AND ABOUT 400 SECONDS, THE BALL FALL VISCOSITY BEING DEFINED AS THE NUMBER OF SECONDS TAKEN BY A STEEL BALL ONE EIGHTH OF AN INCH IN DIAMETER TO FALL THROUGH TWENTY CENTIMETERS OF VISCOSE AT THE ECTRUSION TEMPERATURE 